A method for acquiring synchronization by using a set of predetermined sequences is applicable to various systems, and it is representatively used for detecting a cell identifier in a wireless communication system. A receiving side takes a correlation on a received signal with a plurality of predetermined sequences to calculate a correlation value with the received signal for each sequence, and estimates a transmitted sequence based on per-sequence correlation values. However, the synchronization acquisition process is generally performed without channel estimation. Hence, the noncoherent demodulation is performed. Since the correlation value can be negative, the magnitude or the absolute value of the correlation value is used for the sequence detection process of the received signal.
A synchronization channel receiving method according to the conventional art will now be described. First, the received signal will be referred to as a vector r=[r0r1 . . . rN-1]T. Here, rn (n=0, . . . , N−1) represents an element or entry configuring the received signal vector r, and the index n indicates a time or a subcarrier of an orthogonal frequency division multiplexing (OFDM) system. When n indicates a subcarrier, shows a received signal of the subcarrier n. N corresponding to the length of vector r indicates the length of the synchronization sequence.
A set of a predetermined sequences is called c(k)=[c0(k)c1(k) . . . cN-1(k)]T(k=0, . . . , K−1).
Here, K represents a number of sequences in the sequence set.
The square value D(k) of the correlation value of the received signal r and the sequence k is given as Equation 1.
                              D                      (            k            )                          =                                                                        ∑                                  n                  =                  0                                                  N                  -                  1                                            ⁢                                                c                  n                                      (                    k                    )                                                  ⁢                                  r                  n                  *                                                                          2                                    (                  Equation          ⁢                                          ⁢          1                )            
Here, |◯| represents the magnitude of the complex number, and rn* indicates a complex conjugate of rn.
A sequence transmitted by a transmitter is called [c0(m)c1(m) . . . cN-1(m)], and each element or entry of the transmitted sequence is referred to as a chip. When a channel gain between a transmitting side and a receiving side undergone by cn(m) is set to be an, a relation between a transmitted signal and a received signal is expressed as Equation 2.rn=ancn(m)+wn  (Equation 2)
Here, wn is additive white Gaussian noise (AWGN). Equation 3 is acquired by ignoring AWGN (wn=0) and substituting Equation 2 for Equation 1.
                              D                      (            k            )                          =                                                                        ∑                                  n                  =                  0                                                  N                  -                  1                                            ⁢                                                a                  n                                ⁢                                                                            c                      n                                              (                        m                        )                                                              ⁡                                          (                                              c                        n                                                  (                          k                          )                                                                    )                                                        *                                                                          2                                    (                  Equation          ⁢                                          ⁢          3                )            
In general, c(k)(k=0, . . . , K−1) is set so that the cross-correlation value between the sequences may be small, that is, it may satisfy Equation 4. If an is rarely variable by n, D(k) can be approximated as Equation 5. Therefore, D(k) has a relatively large value when k≠m and D(k) has a relatively large value when k=m, so that the transmitted sequence can be estimated by the receiving side.
                                                                                    ∑                                  n                  =                  0                                                  N                  -                  1                                            ⁢                                                                    c                    n                                          (                                              k                        1                                            )                                                        ⁡                                      (                                          c                      n                                              (                                                  k                          1                                                )                                                              )                                                  *                                                          ->          0                ,                                  ⁢                              k            1                    ≠                      k            2                                              (                  Equation          ⁢                                          ⁢          4                )                                          D                      (            k            )                          ≈                                                                          a                n                                                    2                    ⁢                                                                                    ∑                                      n                    =                    0                                                        N                    -                    1                                                  ⁢                                                                            c                      n                                              (                        m                        )                                                              ⁡                                          (                                              c                        n                                                  (                          k                          )                                                                    )                                                        *                                                                    2                                              (                  Equation          ⁢                                          ⁢          5                )            
However, if an is changed greatly according to n, D(k) can be substantially increased in the case of k≠m and D(k) can be frequently decreased in the case of k=m, and hence the sequence detected by the receiver according to the conventional synchronization channel receiving method may further generate a sequence that is different from that transmitted by the transmitter. That is, when n represents a subcarrier, N is great, and the channel has great frequency selectivity in the OFDM system, so the conventional art increases transmission sequence detecting error probability.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.